The invention relates to a vibration gyroscope of a tuning fork type formed of piezoelectric material to be used as a piezoelectric vibration gyroscope, and a method for adjusting resonance frequencies of the same.
In general, a vibration gyroscope is known as a device for measuring an angular velocity of a rotating object mounting a vibrating object thereon by making use of a phenomenon that Coriolis force which is vertical to both a vector of the angular velocity and that of the vibration exerts on the vibrating object, and has been used as the device for confirming a position of an aircraft, a vessel or a space orbiter.
Recently, the vibration gyroscope has come to be used for various commercial purposes, such as positioning in a car navigation, control of an attitude of an automobile, or detection of deflection of a camera for a VTR or a still picture.
In the aforementioned vibration gyroscope, a driving voltage is impressed upon this device to excite a driving vibration, and a detecting vibration caused by Coriolis force is detected electrically. The vibration gyroscope of the aforementioned type are classified into a Sperry tuning fork gyroscope, a Watson tuning fork gyroscope, a rectangular metal plate tuning fork gyroscope, a cylindrical vibration gyroscope, etc. as shown in xe2x80x9cElasticwave device hand bookxe2x80x9d (OHM Co.Ltd) pp.491 to pp.497.
Heretofore, a piezoelectric vibration gyroscope of this kind has been disclosed in Japanese Patent Applications Laid-Open No.8-128830, in which a tuning fork gyroscope with high performance formed of lithium tantalate is made public.
The aforementioned piezoelectric vibration gyroscope will be explained referring to FIGS. 1A, 1B.
As shown in these drawings, a piezoelectric vibration gyroscope 100 is composed of a base 101 having a rectangular major surface 101 a and right and left arms 102, 103 projecting from both side ends of the base 101 on the same sides thereof, and all these structural elements constitutes a gyroscope of a tuning fork type. The right and left arms 102, 103 are respectively provided with driving electrodes for exciting a vibration and detecting electrodes for detecting the vibration (both the electrodes are not shown).
Next, the operation of the piezoelectric vibration gyroscope mentioned in the above will be explained referring to FIGS. 1A, 1B.
If a driving voltage is impressed upon the electrodes on the right arm 102, the arm 102 vibrates from right to left in a plane running in parallel with the major surface 101a of the piezoelectric vibration gyroscope 100. When the right arm 102 vibrates, the vibration is transmitted to the left arm 103 via the base 101, and the arms 102, 103 start a tangential vibration. That is to say, these arms repeat such movements that the arms 102, 103 are close to and remote from each other in a plane running in parallel with the major surface 101a of the piezoelectric vibration gyroscope 100. The tangential vibration is one of characteristic modes of the piezoelectric vibration gyroscope 100, and functions as a driving vibration mode in this example.
At this time, if the piezoelectric vibration gyroscope 100 is fixed to a rotating object which rotates around the Z axis (a direction of projection of the arms 102, 103) shown in FIG. 1A at an angular velocity of xcexa9, Coriolis forces Fc vertical to the major surface 101a exert on the arms 102, 103.
Accordingly, the vertical vibration is excited in the arms 102, 103 because of Coriolis forces Fc, and thereby these arms repeat such a movement that they are displaced in the opposite directions vertically to the major surface 101a. The vertical vibration is another one of the characteristic vibration modes of the piezoelectric vibration gyroscope 100 also, and functions as a detecting vibration mode in this example.
In order to detect the angular velocity xcexa9 of the rotating object around the Z axis, the vertical vibration of the detecting vibration mode is detected through a difference in a potential between the detecting electrodes formed on the arm 103.
However, on the conventional piezoelectric vibration gyroscope mentioned in the above, since there is no nodal (unmoved) point of both the driving and detecting vibration modes, not only the vertical vibration (the detecting vibration mode) but also the tangential vibration (the driving vibration mode) are excited in the left arm 103. Moreover, since both the arms 102, 103 project on the same side, these arms are situated closely to each other.
As a result, the driving and detecting modes interfere with each other. That is to say, a mechanical coupling occurs between the arms 102, 103. Moreover, a voltage impressed upon the driving electrodes interferes with a detecting current flowing through the detecting electrodes, hence an electrostatical coupling occurs between the driving and detecting electrodes. Accordingly, an electromechanical coupling occurs between the driving and detecting electrodes, which causes a noise interfering with the detection, deteriorates a S/N ratio, and lowers a resolution of the angular velocity.
Accordingly, it is an object of the invention to provide a piezoelectric vibration gyroscope and a method for adjusting resonance frequencies of driving and detecting modes of the same, in which an angular velocity of a rotating object is detected under a satisfactory S/N ratio, and a resolution of an angular velocity is heightened.
According to the first feature of the invention, a piezoelectric vibration gyroscope comprises:
a main body shaped into a rectangular plate and provided with obverse and reverse surfaces functioning as major surfaces, and
first and second groups of three arms projecting from the main body in opposite directions and lying on extensions of the major surfaces,
wherein the main body and the first and second groups of the three arms are formed of piezoelectric material,
the first group of the three arms is composed of two excitation driving side arms excited in an opposite phase and a nonexcitation driving side arm inserted between the two excitation driving side arms,
the second group of the three arms is composed of two vibration detecting side arms vibrating in an opposite phase and a nonvibration detecting side arm inserted between the two vibration detecting side arms,
the two excitation driving side arms are respectively provided with driving electrodes for exciting a tangential vibration vibrating in parallel with the major surfaces, and
the two vibration driving side arms are respectively provided with detecting electrodes for detecting a vertical vibration vibrating vertically to the major surfaces.
Accordingly, when the whole gyroscope is situated on a rotating object and a driving voltage is impressed upon the excitation driving side arms to excite a tangential vibration, the vertical vibration is generated in the excitation driving side arms because of Coriolis force, and the vertical vibration is transmitted to the vibration detecting side arms via the main body to excite the vertical vibration therein.
In the piezoelectric vibration gyroscope according to another aspect of the invention, the main body is shaped into the rectangular plate so that a transmission of the tangential vibration from the excitation driving side arms to the vibration detecting side arms can be suppressed.
Accordingly, even when the tangential vibration is excited in the excitation driving side arms, the main body prevents the tangential vibration from being transmitted to the vibration detecting side arms.
In the piezoelectric vibration gyroscope according to another aspect of the invention, the main body and the first and second groups of the three arms are formed into one united body.
The frequency characteristic of the aforementioned piezoelectric vibration gyroscope is more excellent than that of a piezoelectric vibration gyroscope in which the arms are connected with the main body via joints.
In the piezoelectric vibration gyroscope according to another aspect of the invention, the excitation and nonexcitation driving side arms and the vibration and nonvibration detecting side arms are formed either of Z cut quartz or a Z cut langasite, and have a rectangular shaped cross-section,
each of front, rear, right side and left side surfaces (vertical surfaces, hereinafter) of each of the excitation driving side arms is provided with the driving electrode, which extends from a neighborhood of a starting end of the excitation driving side arm towards a terminal end thereof running along a center line of the vertical surface and maintaining predetermined dimensions, and
each of right and left side surfaces of each of the vibration detecting side arms is provided with a pair of strip shaped detecting electrodes having same dimensions, which extends from a neighborhood of a starting end of the vibration detecting side arm towards a terminal end thereof running along both side edges of the vertical surface and maintaining predetermined dimensions.
If the driving electrodes are so connected with an AC power supply that the driving electrodes situated opposite to each other are in the same polarity and the adjacent driving electrodes are in the opposite polarity, the tangential vibration is excited in the excitation driving side arms.
Moreover, if the detecting electrodes are so connected with a detecting device that the detecting electrodes situated on the same diagonal are in the same polarity and the detecting electrodes situated on the same surface are in the opposite polarity, the vertical vibration in the vibration detecting side arms can be detected.
In the piezoelectric vibration gyroscope according to another aspect of the invention, a length of said driving electrode is forty to seventy percent of that of said excitation driving side arm,
a width of the driving electrode is fifty to seventy percent of that of the excitation driving side arm,
a length of the detecting electrode is forty to seventy percent of that of the vibration detecting side arm, and
double width of the detecting electrode is thirty to fifty percent of a width of the vibration detecting side arm.
Accordingly, in case that piezoelectric material is formed of Z cut quartz or Z cut langasite, displacements of the vibration detecting side arms can be detected with high sensitivity because of a high electromechanical coupling efficient.
In the piezoelectric vibration gyroscope according to another aspect of the invention, the excitation and nonexcitation driving side arms and the vibration and nonvibration detecting side arms are formed of material of one kind selected from X cut quartz, X cut langasite, and 130xc2x0 rotated Y plate lithium tantalate, and have a rectangular shaped cross-section,
each of front and rear surfaces of each of the excitation driving side arms is provided with a pair of strip shaped driving electrodes having same dimensions, which extends from a neighborhood of a starting end of the excitation driving side arm towards a terminal end thereof running along both side edges of the front or rear surface and maintaining predetermined dimensions, and
each of front, rear, right side, and left side surfaces (vertical surfaces, hereinafter) of each of the vibration detecting side arms is provided with a detecting electrode, which extends from a neighborhood of a starting end of the vibration detecting arm towards terminal end thereof running along a center line of the vertical surface and maintaining predetermined dimensions.
Accordingly, if the driving electrodes are so connected with an AC power supply that the driving electrodes situated on the same diagonal are in the same polarity and the driving electrode situated opposite to each other and the driving electrodes situated on the same surface are in the opposite polarity, the tangential vibration is excited in the excitation driving side arms.
Moreover, if the detecting electrodes are so connected with the detecting device that the detecting electrodes situated opposite to each other are in the same polarity, and the adjacent detecting electrodes are in the opposite polarity, an amplitude of the vertical vibration in the vibration detecting side areas can be detected.
In the piezoelectric vibration gyroscope according to another aspect of the invention, a length of the driving electrode is forty to seventy percent of that of the excitation driving side arm,
double width of the driving electrode is thirty to fifty percent of a width of the excitation driving side arm,
a length of the detecting electrode is forty to seventy percent of that of the vibration detecting side arm, and
a width of the detecting electrode is fifty to seventy percent of that of the vibration detecting side arm.
Accordingly, in case that piezoelectric material is formed of X cut quartz, X cut langasite, 130xc2x0 rotated Y plate lithium tantalate or piezoelectric ceramics, displacements in the detecting side arms can be detected because of a high effective electromechanical coupling coefficient.
In the piezoelectric vibration gyroscope according to another aspect of the invention, a whole gyroscope is constructed so as to be symmetrical with respect to both horizontal and vertical axes thereof, and a thickness of the main body is a same as those of the excitation and nonexcitation driving side arms and the vibration and nonvibration detecting side arms.
a thickness of the main body is a same as those of the excitation and nonexcitation driving side arms and the vibration and nonvibration detecting side arms.
Accordingly, a structure of the piezoelectric vibration gyroscope which is free from spurious response and has satisfactory frequency response can be obtained easily.
In the piezoelectric vibration gyroscope according to another aspect of the invention, the piezoelectric vibration gyroscope is provided with the first and second supporting members, wherein:
the first supporting member is situated on the first boundary between the nonexcitation driving side arm and the main body, and the second supporting member is situated on the second boundary between the main body and the nonvibration detecting side arm.
Accordingly, the piezoelectric vibration gyroscope can be supported maintaining a high stability by means of the supporting members fixed to the piezoelectric vibration gyroscope at positions where displacements thereof are extremely small.
In the piezoelectric vibration gyroscope according to another aspect of the invention, the piezoelectric vibration gyroscope is provided with a supporting member situated on a center of gravity thereof.
Accordingly, the whole structure of the piezoelectric vibration gyroscope can be supported with improved stability by means of the supporting member fixed to this device at a center of gravity thereof where the displacement due to the vibration is the smallest.
According to the second feature of the invention, a method for adjusting a difference in a resonance frequency between a tangential vibration and a vertical vibration of a piezoelectric vibration gyroscope, which comprises:
a main body shaped into a rectangular plate and provided with obverse and reverse surfaces functioning as major surfaces, and
first and second groups of three arms projecting from the main body in opposite directions and lying on extensions of the major surfaces,
wherein the main body and the first and second groups of the three arms are formed of piezoelectric material,
the first group of the three arms is composed of two excitation driving side arms vibrating in an opposite phase and a nonexcitation driving side arm inserted between the two excitation driving side arms,
the second group of the three arms is composed of two vibration detecting side arms vibrating in an opposite phase and a non vibration detecting side arm inserted between the two vibration detecting side arms,
the two excitation driving side arms are respectively provided with driving electrodes for exciting a tangential vibration vibrating in parallel with the major surfaces, and
the two vibration driving side arms are respectively provided with detecting electrodes for detecting a vertical vibration vibrating vertically to the major surfaces, comprises the step of:
cutting four corners of the main body.
When the four corners of the main body are cut, lowering of the resonance frequency of the vertical vibration is more noticeable than that of the tangential vibration.